1. Technical Field
The present invention relates to a speaker apparatus.
2. Related Art
FIG. 1 shows a constitution of a related-art general dynamic speaker apparatus.
The speaker apparatus 1 includes; a magnetic circuit 3; a frame 5 attached with the magnetic circuit 3 at a rear portion thereof; a vibrating plate 9 of a cone-like shape in which an edge 7 in a roll-like shape at an outer periphery thereof is fixed to a vibrating plate supporting portion 5a of a front portion of the frame 5, and a voice coil 12 wound around a voice coil bobbin 11 in a cylindrical shape.
The magnetic circuit 3 includes a yoke 15 projecting a center pole 15b in a cylindrical shape at a center of a plate 15a in a shape of a circular plate, a magnet 16 in a ring-like shape fitted to an outer periphery of the center pole 15b, and a top plate 17 in a ring-like shape fitted to be mounted to a front end side of the center pole 15b to interpose the magnet 16 between the top plate 17 and the plate 15a. 
A gap between an inner periphery of the top plate 17 and the center pole 15b serves as a magnetic gap 19 for arranging the voice coil 12.
The vibrating plate 9 is formed with an opening portion 9a for inserting the voice coil bobbin 11 at a center thereof. The edge 7 bonded to an outer peripheral edge of the vibrating plate 9 is fixed to the vibrating plate supporting portion 5a. An attaching flange 7a mounted to an outer periphery of the edge 7 is interposed between a gasket 21 in a ring-like shape pasted to the vibrating plate supporting portion 5a and the vibrating plate supporting portion 5a. 
Further, an inner peripheral portion 9b of the vibrating plate 9 forming the opening portion 9a is fixed to an outer periphery of the voice coil bobbin 11 inserted to the opening portion 9a by adhering or the like.
Further, a center portion of the vibrating plate 9 is pasted with a dust cap 28. The dust cap 28 covers a front side of the voice coil bobbin 11 to prevent dust and dirt from invading the magnetic gap 19.
The voice coil bobbin 11 in the cylindrical shape is fitted to an outer periphery of the center pole 15b movably in an axial direction and is elastically supported by the frame 5 by a damper 25 to restrict movement thereof in the axial direction.
Normally, there is spread the damper 25 forming a bellows structure concentrically with the voice coil bobbin 11.
The damper 25 damps the vibrating plate 9 by restricting displacement of the voice coil bobbin 11 in a radius direction by fixing an outer peripheral edge thereof to a damper supporting portion 5b of the frame 5 and fixing an inner peripheral portion thereof to an outer periphery of the voice coil bobbin 11 and absorbing vibration energy by deforming the bellows in driving the vibrating plate 9.
The frame 5 is normally configured by a structure of providing a plurality of frame openings 5c formed at pertinent intervals along a circumferential direction of the speaker between the vibrating plate supporting portion 5a and the damper supporting portion 5b. The frame opening 5c functions as a vent hole for releasing an air flow produced by a back pressure in driving the vibrating plate 9.
Further, the frame opening 5c not only functions as the above-described vent hole but also constitutes light-weighted formation of the frame 5.
When a sound signal is inputted to the voice coil 12, the above-described speaker apparatus 1 reproduces sound by vibrating the vibrating plate 9 by reciprocally vibrating the voice coil bobbin 11 thereby.
Recently, examples of employing a large-sized speaker for reproducing low frequency sound, such as subwoofer, are increasing in a car-audio system.
When the large-sized speaker apparatus is designed for the car-audio system, a depth dimension of a portion utilized as a cabinet of the speaker apparatus such as a vehicle-mounted speaker cabinet or an inner side of a vehicle door is limited and therefore, it may be subject to thin the speaker apparatus.
However, according to the related-art speaker apparatus 1 in which the voice coil bobbin 11 is elastically supported by the damper 25 as described above, a space of arranging the damper 25 needs to provide between the vibrating plate 9 and the magnetic circuit 3. It is difficult to shorten a dimension in the axial direction of the speaker apparatus in order to provide the space of installing the damper 25.
Further, a stiffness of the damper 25 is normally larger than that of the edge 7 and therefore, mechanical fatigue by a long period of time of use is brought about earlier than in the edge 7 and there is a concern of causing a failure by deteriorating a control function.
Further, there is also a possibility of generating particular vibration or a brazing sound by deforming the bellows in propagating vibration between the contiguous bellows on the damper 25, which conversely effects an influence on the vibration of the voice coil 12 or the vibrating plate 9 to deteriorate sound quality. (refer to, for example, JP-A-2005-191746).
Further, it is a problem for the speaker apparatus how to cool heat generated by the magnetic circuit particularly by narrowing the installing space by thinning the speaker apparatus. A number of proposals have been made for cooling speaker apparatus (refer to, for example, JP-A-2003-299185).